There's the obvious question of what you would like to see in the game, but the better question is what sort of features do like most in game design as a whole: do people like long, horizontal engagements, or tall ones where 3D orientation and positioning matter? Or maybe a mix: Long canyons and valleys with enormous amounts of vertical and horizontal placement options?
There's also a hundred of other ones to ask yourself, but just a few I can think of: do you prefer non-symmetric maps, purposefully biased maps, symmetric ones; balanced maps that aren't symmetric, etc?
And then, there's also the importance of aesthetics, and how they can effect a level. My personal favorites has generally got to be tropical areas which made it into the G.R.A.W. games; they had a less-than-interesting layout, but the aesthetics of having a fairly nice jungle, which I know takes a huge amount of effort in comparison to a few other environments, but when done nicely, it can be very nice. Many players here seem to want snow or desert maps, and I think we're more apt to see the latter, I'd still love to see a few maps based in a few mountain chains in Europe.
In specifics to Wargame, what I would like to see most are a few maps based off MOUT, specifically laid out in a manner which uses this document as a basis for its design:
Modern highways would provide an interesting amount of vertical play regarding tanks; helicopters would become much more viable in an area where instead of having to go into the lower altitude setting and hover, they could instead move around a building, and I'd imagine it would be possible to create buildings within the engine that set infantry on a second floor(As in, once they enter the building, they'll climb up a 'hidden' slope to settle in their firing position).
Another thing I like, is beachhead (Part of my jungle/island/coastal/insect and mosquito infested hell fetish, having lived in a desert and forested mountain areas all my life) assaults/defenses, and it would be especially interesting if a zone could contain a non-controlled CV for either side, like, a command bunker, or, say, a set of landing ships, that in the case of landing units, once destroyed would remove the insertion/reinforcement property associated with the zone, whereas a command bunker once destroyed would result in a minor amount of reinforcement points should the zone be recaptured; and it would certainly help with scenario construction.
Also, the only thing that really gets me about Wargame is that a few of these maps are so flat; look at Blitz from the ground perspective and try to not ton wince: it's like a billiards table. Also, most of the time, infantry combat in-game is fairly bland, as we all tend to avoid towns like the plague unless we're taking them to defend from like, say, Storm Eye, which is a very interesting map to play with 2-3 players due to the significance of the center island in how it influences the flow of the rest of the game. Maps which would promote the concept of combined arms that isn't just flamethrower + meatbags = win would be a lot of fun, especially in the context of MOUT where tanks feel comparable to siege weapons that move on their own power.